U.S. Pat. No. 3,799,362, issued Mar. 26, 1974, discloses and claims a vehicle comprising three pairs of opposed wheels positioned along opposite sides of the vehicle, and wherein the wheels at the center extend beneath the wheels at the opposite ends of the vehicle. In application Ser. No. 115,942, filed Jan. 28, 1980, an undercarriage for supporting and propelling a mechanism is disclosed which includes at least three wheels rotatably supported at spaced points along a frame, with the middle wheel extending below a plane lying tangent to the bottoms of the endmost wheels. Application Ser. No. 112,727, filed Jan. 17, 1980, discloses and claims an interchangeable undercarriage unit also including a middle or center wheel extending below endmost wheels.
Vehicles in corporating the structure disclosed in the above recited applications accomplish the objective of having both short and long wheelbases by means of lower middle wheels. For example, when operated over a hard, smooth surface, the vehicle will rest only on the middle wheels and one pair of endmost wheels determined by the location of the overall center of gravity of the vehicle at a given moment. The effective wheel base of the vehicle comprises the distance between the middle wheels and the pair of the endmost wheels in contact with the surface. Consequently, the effort required to effect steering of the vehicle is substantially reduced over that which would be required if the wheelbase comprised the distance between both pairs of endmost wheels. If the vehicle is operated over an adverse terrain, such as sand, mud or loose dirt, all three pairs of wheels will engage the adverse surface because they will sink into the adverse surface until vehicle flotation occurs. Superior traction will be achieved as each wheel directly contacts the surface. Typically, the wheels will comprise pneumatic tires formed from a rubber compound to enhance flotation and traction.
It has been found in several applications of the vehicle that increased stability would be desirable. In addition, the resilient nature of the pneumatic wheels has caused the vehicle on occasion to bounce or oscillate as the center of gravity of the vehicle is shifted from opposite sides of the middle wheels as a load is transfered to and from the vehicle during operation. This has been found to reduce the efficiency of the vehicle.